Outline

Objective

To preserve facial function is one of the aims in acoustic neuroma surgery. It is also crucial to determine the optimal postoperative strategy for patients with postoperative facial paresis. The aim of this study was to show whether if measurement of intraoperative evoked muscle action potentials of facial muscles has a prognostic value for facial function outcome.

Methods

From 02/00 to 06/03 nervus facialis function was tested in 22 patients after resection of an acoustic neuroma by stimulating the nerve close to the brainstem (BS) and in the meatus acusticus internus (MAI). The change in amplitude of facial muscle action potential (MAP) was classified into 3 groups (75-100%, 10-75%, under 10%, MAP evoked at BS versus MAI) and correlated with the postoperative function of the nerve.

Results

In all but one patient stimulation of the nerve at both sites was possible. In 10 patients there was no or only a mild reduction of the amplitude (75-100%). These patients had no or a mild change in facial nerve function (0-1 grade deterioration according to House and Braakmann) with the exception of one patient with deterioration of 3 grades. 7 patients showed an amplitude reduction to 10-75% of the maximum amplitude in MAI, 2 had a no change in postoperative function, 5 a worsening of 3 grades in House-Braakmann-scale. In the remaining 4 patients the MAP evoked at BS was under 10% of the MAP in the MAI. All these patients had a severe postoperative paresis of facial muscles. Of these patients only one with a complete loss of MAP at the BS showed no improvement at control. In the other cases there was no correlation of intraoperative neurophysiological status with clinical outcome after 4-32 months.

Conclusions

Stimulation of the facial nerve after resection of an acoustic neuroma is a helpful tool to determine the postoperative function of the facial nerve although a reliable prognosis is only possible in the case of reduction of MAP at BS under 10% of MAP in the MAI. All these patients will have a severe facial paresis postoperatively.